This invention relates to a spot-type disc brake, particularly for motor vehicles, with a non-rotating brake carrier to receive the brake torque, said brake carrier being immovable in relation to the brake disc. Brake shoes are arranged on both sides of a brake disc, with a yoke or frame protruding over the brake disc and movably guided in the brake carrier in the direction of the brake disc and being held without clearance by resilient means. The yoke or frame transmits the operating force of an actuating device arranged on one side of the brake disc and acting directly upon one brake shoe, to the brake shoe arranged on the opposite side of the brake disc.
In such spot-type disc brakes the guides of the frame or yoke in the brake carrier are designed with clearance in order to guarantee an easy movability of the movable members in all operational conditions, and in order to avoid high costs arising from special manufacturing tolerances. To avoid rattling noises by vibrations produced when the vehicle is in motion, it is common to .[.tension.]. .Iadd.force .Iaddend.the frame or the yoke .[.relative to.]. .Iadd.against .Iaddend.the brake carrier by resilient means and, thus, overcome the manufacturing tolerances.
From the German published Patent application DT-OS No. 1,905,576 a spot-type disc brake is known wherein the frame at which the actuating device is also arranged is movably supported in the brake carrier in the direction of the brake disc. This is to say that this frame is guided in rectangular grooves which are disposed in the brake carrier on one side of the brake disc, the frame being .[.tensioned relative to.]. .Iadd.forced against .Iaddend.the lower groove wall by spring arms, which are supported at the upper groove wall. The frame is supported at the opposite side of the brake disc by a pin formed in the frame with the pin being disposed in a recess in the backing plate of the brake shoe which is connected to the brake carrier via locking pins. Due to the arrangement of the actuating device and the frame, the center of gravity of the frame is far outside the triangle formed by the connecting lines of the guide points, and, therefore, high forces due to gravity occur with vibrations when the vehicle is in motion which because of the unfavorable leverages necessitate--in order to be supported by the spring arms--that these spring arms be provided with a high spring tension. The unfavorable leverages result from the fact that the distance between the center of gravity of the frame and the center of revolution, which is defined by the pin in the recess of the brake shoe on the opposite side of the brake disc, is considerably longer than the distance between the point of application of force of the spring arms and the center of revolution. The high spring forces, however, produce high surface pressures between the frame and the lower groove wall, and owing to the friction this phenomenon leads to high shifting forces when the brake is actuated, and impedes a reset of the brake shoes--connected with the frame--to the necessary brake lifting clearance after a braking process.